This invention relates to an electro-hydraulic pump control system for controlling displacement of a pump. More particularly, the invention is directed to a method and system for electro-hydraulic pump control that utilizes pump characteristics determined from an operation of the pump.
A pump having a variable displacement capability is well known in the industry to drive an implement or a hydrostatic motor. In an open-loop hydraulic system, a variable displacement pump is used to drive an implement, such as a cylinder or a hydraulic motor, and the fluid pressure from the pump to the implement is controlled by varying the displacement of the variable displacement pump. In a closed-loop hydrostatic system, similarly, a variable displacement pump is used to drive a hydrostatic motor in the forward or reverse direction, and the speed of the hydrostatic motor is controlled by varying the displacement of the pump.
A variable displacement pump generally includes a drive shaft, a rotatable cylinder barrel having multiple piston bores, and pistons held against a tiltable swashplate biased by a centering spring. When the swashplate is tilted relative to the longitudinal axis of the drive shaft, the pistons reciprocate within the piston bores to produce a pumping action. Each piston bore is subject to intake and discharge pressures during each revolution of the cylinder barrel. As the piston bores sweep pass the top and bottom center positions, a swivel force is generated on the swashplate as a result of the reciprocating pistons and pressure carryover within the piston bores. Some hydrostatic pumps have eliminated the actuator and/or cut-off valves by controlling swivel forces and actuator pressure. In order to accurately control the pump displacement, however, it may be necessary to provide a closed logic on the pump displacement and/or pressure, which increases manufacturing cost and reduces reliability.
In a system to control the pump displacement, a pump control signal is often directed through a variable orifice and a fixed orifice to an actuator to change the displacement of the variable displacement pump. The variable orifice is often controlled by a spool valve that is movable in response to a remote signal. In the past, the arrangement for controlling the displacement of a pump required a pressure cut-off, torque limiters, relief valves, or other components. These components increase the size of the arrangement and the manufacturing cost.
For example, U.S. Pat. No. 6,179,570 discloses a variable pump control for a hydraulic fan drive. The pump control includes a load margin valve arrangement, a pressure cutoff valve, and a proportional solenoid valve arrangement. The load margin valve arrangement has a valve that can be moved in response to pressurized fluid from the pump. The pressure cutoff valve also has a valve that can be moved in response to pressurized fluid from the pump. The proportional solenoid valve arrangement has a solenoid and a valve and can be actuated to control fluid flow through the valve by an electrical signal to the solenoid. The pump control, therefore, requires multiple valves.
Therefore, what is needed is a simplified pump control system involving lower manufacturing cost which overcomes one or more of the problems as set forth above.
In one aspect of the invention, a method is provided for controlling displacement of a variable displacement pump coupled to a load. The method includes determining an electrical signal to be applied to a proportional solenoid for a desired pump displacement based on known pump characteristics. The electrical signal is provided to a proportional solenoid. The displacement of the variable displacement pump is controlled based on the electrical signal to the proportional solenoid.
In another embodiment, a method is provided for controlling displacement of a variable displacement pump coupled to a load. The method includes applying an electrical signal of varying amplitude to a proportional solenoid during operation of the variable displacement pump. Displacement of the variable displacement pump is evaluated for different amplitudes of the electrical signal to create reference points for the electrical signal and the pump displacement. The electrical signal to be applied to the proportional solenoid for a desired pump displacement is determined by interpolation.
In yet another embodiment, a pump control system is provided for controlling displacement of a variable displacement pump that receives fluid from a reservoir and is coupled to a load. The pump has minimum and maximum displacement positions and a pressure outlet port. The pump control system includes a displacement changing mechanism and a proportional solenoid valve arrangement. The proportional solenoid valve arrangement is connected to the pressure outlet port of the variable displacement pump and is operative to control fluid flow to and from the displacement changing mechanism. The proportional solenoid valve arrangement includes a three-way proportional valve movable between first and second positions. The first position allows the displacement changing mechanism to be in fluid communication with the reservoir and to be blocked from the pressure outlet port of the variable displacement pump. The second position allows the displacement changing mechanism to be in fluid communication with the pressure outlet port of the variable displacement pump. The proportional solenoid valve arrangement also includes a proportional solenoid operative to provide a variable force to move the proportional valve. A captured spring assembly is disposed between the proportional solenoid and the proportional valve. The captured spring assembly defines minimum and maximum control pressure settings.
In yet another embodiment, a fluid control system is provided. The fluid control system includes a variable displacement pump in communication with a pump control unit, a fluid displacement changing mechanism, and a valve arrangement fluidly connected to the variable displacement pump and operative to fluidly communicate with the displacement changing mechanism. The system also includes a solenoid configured to operate the valve arrangement in response to a control signal input to the solenoid. A range of operation of the variable displacement pump is represented by the control signal based on predetermined system characteristics. The pump control unit is operative to infinitely update the control signal in response to the controller and at least one sensor sampling an operation condition.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.